The inventive concept relates generally to electronic memory technologies. More particularly, certain embodiments of the inventive concept relate to nonvolatile memory devices and related methods of operation.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Examples of volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM). Examples of nonvolatile memory devices include electrically programmable erasable read only memory (EEPROM), mask read-only memory (MROM), and programmable ROM (PROM).
Flash memory is a type of EEPROM that is currently used in many applications for long term data storage. For example, flash memory devices are commonly used to store voice and image data in electronic devices such as computers, mobile phones, personal digital assistants (PDAs), digital cameras, camcorders, voice recorders, MP3 players, handheld personal computers (PCs), gaming machines, facsimile machines, scanners, and printers.
In recent years, there has been a general demand to increase the amount of data storage provided by flash memory devices and other forms of nonvolatile memory. One approach that has been adopted for this purpose is to design flash memory cells capable of storing more than one bit of data. A flash memory cell designed to store one bit of data is generally referred to as a single level cell (SLC), and a flash memory cell designed to store more than one bit of data is generally referred to as a multi-level cell (MLC). As the number of bits stored in each memory cell increases, stored data may become less reliable because a greater level of operational precision is required to store more bits per cell. Accordingly, researchers are engaged in continuing efforts to improve the reliability and other performance characteristics of MLCs.